London - Novak Djokovic and Serena Williams are the International Tennis Federation's world champions for 2013.
Djokovic captured the men's award for the third successive year, and Williams took the honor for the fourth time.
Djokovic started the year by winning a third straight Australian Open and was runner-up at Wimbledon and the U.S. Open. The 26-year-old Serb finished the season No 2 in the ATP rankings with seven tour titles.
The 32-year-old Williams won the French Open and US Open in 2013 to end the year No 1 in the WTA rankings for the first time since 2009.
American twins Bob and Mike Bryan were named men's doubles world champions for the 10th time in 11 years, while Sara Errani and Roberta Vinci of Italy took the women's doubles award.